missing: ClockMock using @group annotation

[ComaVN]

According to the documentation, the @group time-sensitive annotation is the preferred way to use the ClockMock in unittests.

However, this does not work out of the box, without registering Symfony\Bridge\PhpUnit\SymfonyTestsListener or using simple-phpunit. This should probably be explained in the documentation. (The 3.2 documentation doesn't mention it's required for using the ClockMock feature, and the 2.8 documentation doesn't even mention simple-phpunit at all, and I can't find it in vendor/bin)

See https://github.com/ComaVN/symfony-phpunit-bridge-clockmock for a test case

See also symfony/symfony#21612